Failed to establish shared memory mapping

[Martin van Es]

Hi Duncan,

Thx for your lengthy answer.
I'm using Kubuntu Wily with custom built kernel 4.3.0 (but the same happens
when booting the ubuntu kernel).
I don't use apparmor and selinux is disabled according to getenforce.

I use kubuntu-backports repository, so as for versions, I'm at plasma
5.4.3, framework 5.15 and apps 15.08.2

Best regards,
Martin

On Wed, Nov 18, 2015 at 2:31 AM, Duncan <1i5t5.duncan at cox.net> wrote:

> Martin van Es posted on Tue, 17 Nov 2015 12:50:35 +0100 as excerpted:
>
> > Hi,
> >
> > I've searched high and low but couldn't find a satisfactory answer to
> > the question: why do all KDE/Plasma apps warn "Failed to establish
> > shared memory mapping, will fallback to private memory -- memory usage
> > will increase"?
> >
> > I have /dev/shm mounted (tmpfs) and /dev/shm has drwxrwxrwt mode bits,
> > /run/shm is a symbolic link to /dev/shm
> >
> > What I find curious is that when I start the same app as root it doesn't
> > show the warning, but I can't for the life of me understand why I can't
> > establish shared memory as a user and can as root?
> >
> > /dev/shm contains file that have pulse-shm in their name, and ipcs -a
> > shows me many shared memory segments?
> > So why can't KDE apps establish shared memory?
>
> This /may/ be a result of some sort of security measures your distro has
> setup.  Unfortunately you didn't mention the distro and version you're
> running, but I've not seen such warnings here, on Gentoo/~amd64.
>
> Also, you didn't mention what version of kde/plasma.  With many distros
> switching to kde-frameworks-5 and plasma-5, while others are still on
> kde4, and even where the switch to 5 has taken place, individual apps may
> remain kde4 based for the time being, this could be important, as well.
>
> FWIW, kde4 here, tho I have most of a minimal kde-frameworks-5/plasma-5
> installed for easier testing, lacking only the few bits that can't be
> installed along with the kde4 versions, so I can keep what's configured
> and working, while quickly switching to the new versions for testing when
> I have time.
>
> As for the warning itself, I don't believe it actually refers to shm.
>
> KDE (at least kde4, and kde3 before it, and I'd guess plasma5 does
> something similar) normally starts up using a special initialization
> sequence that starts one process and then forks several others off it,
> doing it in such a way that they can share the same library (elf *.so
> shared objects) address space, etc, thus allowing shared libraries with
> faster launching and lower memory usage, even where security measures
> such as memory-space randomization would normally force separate
> applications to use their own separately randomized library addresses for
> the same libraries, making it impossible to share the same library
> address space and increasing memory usage.
>
> I'd guess that this isn't working in your case for whatever reason, very
> possibly due to additional security measures taken by your distro.  If
> so, it really doesn't have anything to do with tmpfs or /dev/shm and its
> permissions, but rather, with whatever additional security measures your
> distro is enforcing.
>
> --
> Duncan - List replies preferred.   No HTML msgs.
> "Every nonfree program has a lord, a master --
> and if you use the program, he is your master."  Richard Stallman
>
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